1. Fast retrigger path
What threshold level we need for the fast trigger path?

2. Simulations - Old transistor
Schematic
Simulation
Trigger path
Current schematic
To IGBT
Retrigger path
Fast retrigger path :
MOSFET Reference
2N6782
Continuous drain current
3.5A
Pulsed drain current
14A
Turn-ON Delay Time
15ns
VGS(th) V
This pulse has the voltage as variable parameter.

3. Vgsth for old and new Mosfet
Mosfet IRF7452 (New schematic)
Mosfet 2N6782 (Old schematic)
Voltage at the secondary of the pulse transformer
Vds of the Mosfet
Input voltage = 4.1V
Input voltage = 4.2V
Input voltage = 6V
Input voltage = 6.1V
Complementary information :
-> Length of the pulse = 6 us for both

4. Switching time 100ns between the input pulse and the Mosfet switching
Trigger path
Retrigger path
100ns between the input pulse and the Mosfet switching
Indicator
Circuit
Propagation delays
IC4
HEF4072B
55ns
IC3
HEF4528B
70ns
IC1
HEF4049
25ns T1
2N6782
15ns
Total
165ns

5. IPOC waveforms Complementary information :
-> The values given below must be multiplied by 10
MKD RTRIG.B1
MKB RTRIG.B2
Input signals to the PTM.
Very low voltage (between 3V and 4V)

6. MKBH – data coming from Viliam
MKBH: Ch1,2 = Cts1, Cts2; Ch3,4 = retrig OUT a,b
left: normal pulse at 7.1 TeV with late discharge of accumulated charge
right: big sparking and its coupling to RB output (> 6V peak)

7. Improvements
Change the MOSFET in order to reduce the switching sensibility(Vgs).
Replace by another with higher Vgs.
IPOC :
Increase the voltage level in order to be superior to the value of sparking(>6V)
=> It will be more judicious to have an important difference between the voltage sparking (>6V) and the threshold. If we have to chose between 7.5V and 10V, 10V will be more careful.